I’m new to artics. Iv’e just started a job on containers. The first trailer I had when it was empty was really difficult to slow down smoothley. The brakes would be really grabby and sharp. much like if the brake pedal was just an on/off switch also it would make a clunking noise and jerk the tractor unit.
A week or so after I started I swapped trailers and the new trailer was fine. Now I have swapped trailers again and the problem is back although not quite as bad the symptoms are the same.
This is the load sensing valve that’s playing up. Basically the heavier the load on the trailer the sharper the brakes become so you only have to press the brake pedal as much as you would if you were empty. 9 times out of 10 the brakes between the unit and the trailer are fine but sometimes you are going to get a real grabby trailer. Did you notice it was much better with a heavy load on it?
It sounds as though there may be a problem with the load sencing valve.
Just like the valve is called it detects what weight is on the vehicle,cars ,vans ,trucks buses ,all have them.It sounds like it may be sticking and is detecting what it thinks is a full load and providing the brake effort required to slow the truck/trailer combination,hence the grabbing brakes.
The trailer needs to be checked by a fitter as its not really safe to travel with this defect asap.There is a risk when travelling empty with a truck/trailer (especially when the road is damp) of the trailer brakes locking up causing the trailer to run wide.
yeah it sounds like this is the problem because the heavier the load then the problem goes away. its not the same trailer as the first one I had but it is one of the older looking ones. all the gear is ■■■■ where I work
If you know what a load sensing valve looks like you can fix this yourself quite easily, on the (usually) middle axle of a tri axle there will be a rod attached to the axle beam that goes up to another rod, this second rod goes back into the load sensing valve, if the 2nd (horizontal) rod has a bend in it, this will confuse the LSV into thinking it has more weight on it than it really has, so it will apply more pressure to the trailer brakes, if it is bent, straighten it, if it isn’t, check the rubber bushes where the two rods meet, if they’re worn it will cause the same thing, I wouldn’t advise bending it yourself if it’s all straight, it only takes a very small change in the angle of the horizontal rod to change things dramatically, bend it too far & you could end up with no trailer brakes at all
Both of our rentals have this problem,more so when coupled up to my Actros. One is slightly worse than the other, just a dab on the brakes would have 'em locking up when empty and would stop dead from about 15mph…great fun in heavy traffic
Wheel Nut:
try to get into the habit of dumping the air suspension before you lift a loaded box off and put another on, it often helps
That’s a good thing to do, it also protects your shock absorbers, it can be difficult in some docks because you can’t walk around the lorry once you’re in place, you need to be sure that you won’t drag a mudflap under a tyre & rip the wing off
Definitely sounds like the lsv. The clunk and jerk you’re experiencing is because the back half of the trailer is stopping but the unit is still pulling forward. Get the fitter to check it asap, and get him to look at the locking pins too, as they’ve been trying to stop a unit and half a trailer from detatching. Trust me, the last thing you want on a Friday afternoon when you’ve loaded a heavy 20, is to find out the pins broke and the trailer won’t stretch.
joedwyer1:
it would make a clunking noise and jerk the tractor unit
how do I fix it, whats wrong with it?
The clunk & jerk could also be caused by a worn 5th wheel pin on the trailer. This allows slight movement within the 5th wheel jaws, so when the trailer brakes grab it takes up the slack in the coupling.
It is also possible the unit 5th wheel jaws have not been adjusted, as they should be, to compensate for wear. When pulling a trailer with a good pin it may be virtually unnoticeable, but when a worn pin is coupled, you’ve then got a double whammy effect so to speak.
To put it in simple terms, think of shoving a 3/4" pipe through a 1" hole.
(I nearly used another analogy involving ladies of the night, but as this is a family show, thought best not).
If the trailer has a manual lower and raise handle that has to be pushed in to operate the ststem make sure that the handle is pulled out being left in will not let the load senseing valve do its job because it is shut off by the handle being left in this will increase pressure through the footbrake system and cause grab and bounce when empty .
